Julius neumark



UNITED STATES PATENT Y rrrc JULIUS NEUMARK, on NEW YORK, N. Y.

PROCESSO F EXTRACTING'TIN FROM TIN-PLATE WASTE.

SPECIFICATION forming part of Letters Patent No. 603,200, dated April 26, 1898.

Application filed September 10, 1897.

To all whom it may concern:

Be it known that I, JULIUS NEUMARK, a citizen of the United States, and a resident of the cityof New York, in the county and State operations and results and to make unneces sary the frequent renewal of the material used as the electrolyte, as is required in operating the processes now in vogue. These prior processes consist, stated in general terms, in immersing the tin-scrap in an acid or an alkaline bath which will attack the tin, especially when under the influence of an electric current passing through the bath,with the result that the tin is set free and depositedv at the cathode of the electric circuit. Heretofore in such electrolytic processes several very objectionable phenomena from a practical and economical point of View have de- "veloped. Thus after the electricity has acted for but a short time tin ceases to be set free and deposited, so that the process is short lived. Furthermore, the baths offer great resistance to the electric currents after the process has been in operation a short time by reason of the tin salts which are taken up thereby, and if the strength of the current be increased dangers arise and iron may be deposited. The result is that these processes have been irregular in their operation and required the frequent renewal of the electrolyte employed. These disturbances and objectionable features are especially frequent and manifest when a caustic alkaline bath is employed as the electrolyte, for after the electric current has operated for a little while an alkaline tin salt is formed and becomes dissolved in the bath, with the result that the resistance of the electrolyte to the passage of the current rapidly increases, and the tin ceases to be set free and deposited at the oathode. At the same time a certain amount of the caustic alkali is by the carbonic acid of the air converted into a carbonate and so be- Serial No. 651,243. (No specimens.)

comes lost to the electrolytic process. If the electrolyte be replaced by a fresh bath after the process has ceased to operate satisfactorily, a large amount of tin is lost along with the discarded electrolyte in the form of an alkali stannate, which, if the attempt should be made to recover it by evaporation, would be impure and worthless. Further, should it be attempted to force the process to successfully operate by largely increasing the voltage of the electric current new dangers arise, as oxygen and hydrogen are then set free and explosions become liable,especially where the process is carried on in closed vessels or receivers. These evils are entirely avoided by means of the process which I have invented and which I will now describe and by means of which the electrolyte is preserved as a good conductor of electricity.

In describing my process I will assume that a bath of caustic soda is used as the electrolyte and the tin-scrap or the material from which the tin is to be recovered is placed in the bath and so connected as 'to become the anode of the electric circuit. When the current is established, tin oxid is set free at the anode and is acted upon by the alkali in the bath, forming a sodium stannate, and at the same time metallic tin is set free at the cathode. This action continues for a time; but finally the electrolyte bath becomes so charged with sodium stannate that the process ceases, as has been described, in a great measure or entirely. When this takes place, phosphoric acid is added to the bath, with the result that a reaction takes place between the sodium stannate and the phosphoric acidsodium phosphate, tin oXid, and water bein g formedthe tin oXid being precipitated. At the same time whatever of sodium carbonate there may have been in the bath is converted into sodium phosphate. Sufficient calcium oxidis then added to the bath to react 'upon the sodium carbonate and convert it into sodium phosphate, which is precipitated. At the same time sodium oxid is formed, and that in the presence of the water of the bath is converted into caustic soda, thus reviving the bath without withdrawing it, when the process of recovering the tin from the tin-waste may be continued. The tin oxid which is first precipitated is removed from the bath and the tin recovered mechanically, as by the well-known melting process. The precipitated calcium phosphate is drawn off and may be used either in the preparation of new quantities of phosphoric acid in the well-known manner or as a fertilizer.

The process, so far as my invention is concerned, is indicated by the following equation, viz:

3i Ia SnO (sodium stannate) +2H PO (phosphoric acid) QYa JO, (sodium phosphate) +3S11O (stannic acid) +3H O (water).

EZVa PO (sodium phosphate) BCaO (calcium oxid) 8Na O (sodium oxid) Ca;,(l?O (calcium phosphate).

The reaction above indicated takes place in the presence of sufficient water to form a bath.

Having thus described my invention, what I claim, and desire to secure by Letters Patent, is-

1. The process of regenerating an alkaline electrolyte charged with salts of tin, which consists in adding phosphoric acid to the electrolyte and, after the reaction which takes place is complete, adding calcium oxid to the electrolyte, substantially as and for the purposes hereinbefore set forth.

2. The herein-described process of recovering tin from tin-waste and the like, which consists in subjecting the tin-waste to the conjoint action of a current of electricity, and a 

